On at least one RCI ship the pool staff has begun enforcing the rules regarding not reserving chairs. The attendants are putting stickers with the time on them on chairs which have been tagged with the telltale marks of the chair hog... a pair of sandals (for two chairs - one sandal on each chair), or the more common paperback book. They then come back a bit later and if the chair is still empty they bag up the items and take them away. I think they are giving 45 minutes grace time.
I don't know if this is fleetwide or not. I guess I'll see in a couple weeks.